This proposal is from three NIH funded investigators interested in understanding how structural and functional organization of the nervous system arises during development and changes with experience. The studies here focus on the development of neuronal connectivity at the level of individual cells, and thus require microscopy techniques with high resolution. We are requesting funds to purchase a state-of-the-art confocal/multiphoton system that will acquire high-resolution images, and which will enable us to image neuronal structures in the living animal over days. Many of the projects in the proposal are collaborative between the three investigators. They include in vivo live imaging studies of the neuromuscular junction in development and disease (Lichtman, Sanes), studies of the development of connectivity between the retinas and its central targets (Sanes, Lichtman, Wong) and formation of synaptic circuitry in the retina (Wong, Sanes). This microscope system will be housed in the newly renovated Bakewell Neurolmaging Laboratory, a shared facility immediately adjacent to the laboratories of the three investigators. Lichtman directs the facility with day to day technical support from an engineer, S. Turney, and an experienced microscopist, D. Oakley who is in charge of the management and upkeep of the instruments and training of new users. The device will have long-term institutional support from an endowment to the Neurolmaging laboratory. It will be available to other members of the Neuroscience community at Washington University, particularly for exploring and developing new optical imaging tools.